Field of the Invention
The present disclosure generally relates to positive airway pressure therapy. More particularly, the present disclosure relates to valves (e.g., anti-asphyxia valves, constant flow valves) for use in positive airway pressure therapy.
Description of the Related Art
Respiratory disorders deal with the inability of a sufferer to effect a sufficient exchange of gases with the environment, leading to an imbalance of gases in the sufferer. These disorders can arise as a pathological consequence of an obstruction of the airway, insufficiency of the lungs in generating negative pressure, an irregularity in the nervous function of the brain stem, or some other disorder. Treatment of such disorders is diverse and depends on the particular respiratory disorder being targeted. In the first instance, a constriction of the airway, otherwise known as an obstructive apnea or a hypopnea (collectively referred to as obstructive sleep apnea or OSA), can occur when the muscles that normally keep the airway open in a patient relax during slumber to the extent that the airway is constrained or completely closed off, a phenomenon often manifesting itself in the form of snoring. When this occurs for a significant period of time, the patient's brain typically recognizes the threat of hypoxia and partially wakes the patient in order to open the airway so that normal breathing may resume. The patient may be unaware of these occurrences, which may occur as many as several hundred times per session of sleep. This partial awakening may significantly reduce the quality of the patient's sleep, over time potentially leading to a variety of symptoms, including chronic fatigue, elevated heart rate, elevated blood pressure, weight gain, headaches, irritability, depression, and anxiety.
Obstructive sleep apnea is commonly treated with the application of continuous positive airway pressure (CPAP) therapy. Continuous positive airway pressure therapy involves delivering a flow of gas to a patient at a therapeutic pressure above atmospheric pressure that will reduce the frequency and/or duration of apneas and/or hypopneas. This therapy is typically delivered by using a continuous positive airway pressure device (CPAP device) to propel a pressurized stream of air through a conduit to a patient through an interface or mask located on the face of the patient. The stream of air may be heated to near-body temperature. In some configurations, the stream of air may be humidified. In some such configurations, the stream of air may be humidified by forcing the stream of air to travel through a humidification chamber containing water and a heater for heating the water. In such configurations, the heater encourages the evaporation of the water, which in turn partially or fully saturates the stream of air with moisture. This moisture may help to ameliorate discomfort and/or mucosal tissue damage that may arise from the use of unhumidified CPAP therapy.
During exhalation, the patient's exhaled gases typically flow out of bias flow holes located on the interface, on the connection between the interface and the conduit, or elsewhere in the CPAP circuit (where ‘circuit’ here is defined as the passageway extending from the inlet of the blower to the interface outlet on or within the interface). Such holes are typically made relatively small to reduce noise, and in use the exhaled gases are pushed through the ports or holes by the gases incoming at therapeutic pressure at rates sufficient to keep CO2 rebreathing at acceptable levels. However, under relatively low pressure conditions, for example, when the patient is not receiving therapy, gases exhaled by the patient may not be able escape from such holes at such rates, and additionally a larger volume of exhaled gases may become entrained in the CPAP circuit on the way out to the flow generator/blower inlet. The combination of these two problems may elevate CO2 rebreathing by the patient to unacceptable or undesirable levels.